Oil Spill Hangover

January 08, 2004, vol. 29, no. 1
By Marianne Meadahl

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The ecological consequences of oil spills are longer-term and broader-scale than previously thought, say researchers studying the effects of the most high profile oil spill in recent times - the 1989 Exxon Valdez oil spill in Prince William Sound, Alaska.

A paper co-authored by SFU biology research associate Daniel Esler and published in the Dec. 19 issue of Science shows that the environmental impact went far beyond the hundreds of thousands of sea birds, marine animals an organisms killed in the first days and months following the spill.

Oil continued to contaminate habitats and food chains for more than a decade.

Before the Exxon Valdez, the impact of oil spills was assumed by researchers to be related to their immediate and visible effects. Esler says the unexpected persistence of toxic subsurface oil that became trapped among sand and rocks led to chronic exposure of wildlife.

The Exxon Valdez disaster struck a particularly pristine environment with a highly visible wildlife community. More than 42 million litres of crude oil contaminated some 2,000 kilometers of shoreline.

“People still remember the oily ducks and otters, those graphic images that showed the devastation in the days and weeks after the spill,” says Esler, who was working as a researcher for the U.S. Geological Survey in Anchorage at the time of the disaster. Esler remained in the region for the next dozen years, eventually becoming part of a massive research project to track the spill's long-term fallout.

With colleagues from the U.S. and Canada, including lead author Charles Peterson from the University of North Carolina, he conducted extensive field research well into 2003. “It is remarkable to see that there is still oil out there after all of these years, and even more remarkable to see the subsequent effects on wildlife populations and communities,” he says.

Researchers say chronic, delayed and indirect long-term impacts must be considered when evaluating consequences or analyzing risks associated with oil pollution or other forms of environmental contamination.

In Prince William Sound, substantial amounts of oil remained in subsurface reservoirs under coarse, inter-tidal sediments, protected from weather and retaining their toxicity, becoming “an enduring route of entry into many food chains” for years.

Exposure to the oil in streams by incubating pink salmon eggs led to an increased mortality in each of at least four years after the spill. Similarly, elevated mortality due to the effects of persistent oil continued for years among sea otters and harlequin ducks. A multitude of indirect long-term impacts affected numerous shoreline plants and invertebrates.

Esler says such consequences highlight the need to reconsider the approach to ecological risk assessment. Such data could be useful when considering oil and gas development on the coast of B.C., he suggests. “If there is a silver lining, it's the fact that we are able to learn about the large-scale disastrous effects and better consider how to approach such consequences as they arise,” notes Esler, who currently has several other research projects on migratory birds under way in SFU's centre for wildlife ecology.

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